1. Field of the Invention
The present invention relates to a method for producing multi-layered chip inductors, in which a large number of external electrodes can be readily formed.
2. Description of the Related Art
A conventional method for producing chip inductors will be explained with reference to FIGS. 10 to 12.
First, a slurry of a magnetic ceramic material is applied to the surface of a base film, dried, and then stripped from the base film to obtain a magnetic green sheet (not shown in the figures). In the ceramic arts, the term "green" generally refers to a ceramic part in its unsintered state, as explained on pages 181-185 of Engineering Materials Handbook: Ceramics and Glasses, Vol. 4, 1991, ASM International. Green sheet pieces 1b having a predetermined size are then prepared by cutting the magnetic green sheet. A via hole 2 is made at a predetermined position on each of the green sheet pieces 1b. A coil-shaped internal conductor pattern 3 is printed, for example, using a paste essentially consisting of Ag, at a predetermined position on each of the green sheet pieces 1b. A predetermined number of the green sheet pieces 1b are laminated to form a coil spiralled in the laminating direction, as is shown in FIG. 10. Electrical continuity between the printed coil-shaped internal conductor patterns 3 of the green sheet pieces 1b is achieved through the via holes 2, as is shown by the dotted lines in FIG. 10. A predetermined number of green sheet pieces 1a on which no conductor pattern is printed are provided above and below the laminated green sheet pieces 1b and are pressed to adhere to one another and to adhere to the green sheet pieces 1b.
In a practical manufacturing process, large-area green sheet pieces having a plurality of coil-shaped internal conductors are used for preparing a green ceramic laminate 4 comprising a group of chip-shaped laminates, shown in FIG. 11. The green ceramic laminate 4 is cut along the dotted lines 5 and 6 to obtain chip-shaped green ceramic laminates 7 having a structure shown in FIG. 12. Each end 3a of the coil-shaped internal conductors 103 formed inside the chip-shaped green ceramic laminates 7 is exposed on the corresponding cut face.
Each of the chip-shaped green ceramic laminates 7 is then fired. To obtain a multi-layered chip inductor, external-electrode-paste layers 8 are formed on the cut faces, which are parallel to the lamination direction of the fired chip-shaped ceramic laminate 7 so that the external-electrode-paste layers 8 electrically connect to the corresponding ends 3a of the coil-shaped internal conductor 103, as is shown in FIG. 12.
However, according to the above structure, the ends 3a of the coil-shaped internal conductor 103 are located inside the green ceramic laminate 4, i.e., exposed on the cut faces of each chip-shaped laminate 7. Therefore, for producing a multi-layered chip inductor having the above structure, the following procedure is required: the green ceramic laminate 4 is cut into chip-shaped laminates 7 so that each end 3a of coil-shaped internal conductors 103 is exposed on a cut face; and the external-electrode-paste layers 8 are formed on the cut faces having the exposed ends 3a at chip-shaped laminates 7. Thus, disadvantageously, a jig, an extra manufacturing step, and longer processing time are required for forming the external-electrode-paste layers 8 on the corresponding cut faces of each chip-shaped laminate 7.